Polymer extraction methods

ABSTRACT

Polymer extraction methods are disclosed.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Patent Application Ser. No. 60/401,498, filed Aug. 6, 2002,and entitled “Polymer Extraction Methods,” and U.S. Provisional PatentApplication Ser. No. 60/428,963, filed Nov. 25, 2002, and entitled“Polymer Extraction Methods,” the entire contents of both of which arehereby incorporated by reference.

TECHNICAL FIELD

The invention relates to polymer extraction methods.

BACKGROUND

A polyhydroxyalkanoate (“PHA”) can be extracted from biomass havingcells that contain the PHA. Generally, this process involves combiningthe biomass with a solvent for the PHA, followed by heating andagitation. Typically, this provides a system including two phases, withone phase being a solution that contains the solvent and the PHA, andthe other phase containing residual biomass with cells containing areduced amount of the PHA. Usually, the two phases are separated, andthe PHA is then removed from the solvent.

SUMMARY

In general, the invention relates to polymer extraction methods.

In one aspect, the invention features a method of separating a polymerfrom a biomass containing the polymer. The method includes contactingthe biomass with a solvent system to provide a residual biomass and asolution. The solvent system includes a solvent for the polymer and aprecipitant for the polymer, and the solution includes the polymer, thesolvent for the polymer and the precipitant for the polymer. The methodalso includes applying a centrifugal force to the solution and residualbiomass to separate at least some of the solution from the residualbiomass.

In another aspect, the invention features a method of separating apolymer from biomass containing the polymer. The method includescontacting the biomass with a solvent system to provide a residualbiomass and a solution including the polymer and the solvent system, andseparating at least some of the solution from the residual biomass. Themethod also includes adding a precipitant for the polymer to thesolution to remove at least some of the polymer from the solvent system.

In a further aspect, the invention features a method of separating apolymer from biomass containing the polymer. The method includescontacting the biomass with a solvent system to provide a residualbiomass and a solution that includes the polymer and the solvent system.The solution has a polymer concentration of at least about two percentand a viscosity of at most about 100 centipoise. The method alsoincludes separating at least some of the solution from the residualbiomass.

In one aspect, the invention features a method of separating a polymerfrom biomass containing the polymer. The method includes contacting thebiomass with a solvent system to provide a residual biomass and asolution. The solvent system includes a solvent for the polymer, and thesolution includes the polymer and the solvent for the polymer. Thesolvent for the polymer may have a boiling point greater than 100° C.The method also includes separating the polymer from the residualbiomass.

In another aspect, the invention features a method of separating apolymer from biomass containing the polymer. The method includescontacting the biomass with a volume of a solvent system to provide aresidual biomass and a solution including the polymer and the solventfor the polymer, and separating at least some of the solution from theresidual biomass. The method also includes adding a volume of aprecipitant for the polymer to the separated solution to remove at leastsome of the polymer from the solution. The volume of the precipitantadded is less than about two parts relative to the volume of the solventsystem.

In a further aspect, the invention features a method of separating apolymer from a biomass containing the polymer and biomass impurities.The method includes contacting the biomass with a precipitant for thepolymer to remove at least some of the biomass impurities from thebiomass containing the polymer and the biomass impurities, therebyproviding a purified biomass containing the polymer. The method alsoincludes contacting the purified biomass with a solvent system toprovide a residual biomass and a solution including the polymer and thesolvent for the polymer.

In another aspect, the invention features a method of separating apolymer from the biomass containing the polymer and biomass impurities.The method includes pre-treating the biomass chemically to remove atleast some of the biomass impurities from the biomass containing thebiomass and the impurities, thereby providing a purified biomasscontaining the polymer. The chemical treatments include manipulation ofpH, temperature and contact time with or without the presence ofadditional chemicals such as surfactants, detergents, enzymes or similarmaterials that can aid removal of the biomass impurities. The methodalso includes contacting the purified biomass with a solvent system toprovide a residual biomass and a solution including the polymer and thesolvent for the polymer.

In one aspect, the invention features a method of separating a polymerfrom a biomass containing the polymer. The method includes contactingthe biomass with a solvent system under countercurrent flow conditions.

In another aspect, the invention features a method of separating apolymer from a biomass containing the polymer. The method includescontacting the biomass with a solvent system using a one-stage processthat forms a PHA phase and a residual biomass phase. The ratio of volumeof the solvent system present in the PHA phase to volume of the solventsystem contacted with the biomass is at least about 0.8.

In a further aspect, the invention features a method of separating apolymer from a biomass containing the polymer. The method includescontacting the biomass with a solvent system using a one-stage processthat forms a PHA phase and a residual biomass phase. The ratio of volumeof the solvent system present in the residual biomass phase to volume ofthe solvent system contacted with the biomass is at most about 0.2.

In certain embodiments, the methods can extract polymer (e.g., PHA) frombiomass in relatively high yield. In some embodiments, a relatively highyield of polymer (e.g., PHA) can be extracted from biomass without usingmultiple stages (e.g., with a one-stage process).

In some embodiments, the methods can extract relatively pure polymer(e.g., PHA).

In certain embodiments, the methods can use solvent(s) and/orprecipitant(s) in a relatively efficient manner. For example, arelatively high percentage of the solvent(s) and/or precipitant(s) usedin the methods can be recovered (e.g., for re-use).

In some embodiments, the methods can have a reduced environmentalimpact.

In certain embodiments, the methods can extract the polymer atrelatively high space velocity (e.g. at high throughput with overall lowresidence time in process equipment).

In certain embodiments, the methods can result in a relatively smallamount of undesirable reaction side products (e.g., organic acids). Thiscan, for example, decrease the likelihood of corrosion or otherundesirable damage to systems used in the methods and/or extend theuseful lifetime of such systems.

In some embodiments, the methods can provide relatively high volumetricthroughput (e.g., by using a one-stage process).

In certain embodiments, the methods can provide relatively high solventrecovery.

In certain embodiments, the process can be performed with one-stagedevice (e.g., a countercurrent centrifugal contacter).

In some embodiments, a relatively low viscosity residual biomass isformed (e.g., using countercurrent conditions), which can enhancesubsequent processing such as stripping of residual solvent andconcentration of the solids content (e.g. by evaporation, filtration ordrying).

Features, objects and advantages of the invention are in thedescription, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flow diagram of an embodiment of a method of extracting PHAfrom a biomass with cells containing PHA;

FIG. 2 is a flow diagram of a portion of an embodiment of a method ofextracting PHA from a biomass with cells containing PHA; and

FIG. 3 is a graph showing viscosity and polymer content from ExampleIII.

DETAILED DESCRIPTION

FIG. 1 is a flow diagram of an embodiment of a process for extracting aPHA from biomass having cells that contain the PHA. A slurry is providedthat contains the biomass and water. A solvent system is added to theslurry to form a mixture that contains the slurry and the solventsystem. The mixture is agitated (e.g., stirred) to provide a combinationthat includes two phases. One phase is formed of a solution containingthe PHA and the solvent system with trace amounts of biomass (“the PHAphase”). The second phase is formed of residual biomass having cellswith reduced polymer content, water and a carry over portion of thesolvent system (“the residual biomass phase”). The two phases includedin the combination are separated using an appropriate device thatexploits centrifugal force to facilitate the separation (e.g. disccentrifuge, bowl centrifuge, decanter centrifuge, hydroclone,countercurrent centrifugal contacter). Optionally, one or more solventscan be added to the device that exploits centrifugal force to facilitatethe separation. A precipitant for the PHA is added to the PHA phase toform a mixture that contains the PHA phase and the precipitant. Themixture is agitated (e.g., stirred) to form a combination that containsprecipitated PHA, the solvent system and the precipitant. In certainembodiments, the solvent system and the precipitant are miscible whichresults in the combination (precipitated PHA, solvent system andprecipitant) having two phases (e.g., one phase containing theprecipitated PHA, and one phase containing the solvent system andprecipitant). The combination (precipitated PHA, solvent system andprecipitant) is separated (e.g., by filtration or using centrifugalforce) to provide the isolated, extracted PHA.

The process in FIG. 1 can be referred to as a one-stage process. Ingeneral, a one-stage process is a process in which only onecentrifugation step is used during separation of the polymer (e.g., PHA)from the biomass. In general, a multi-stage process refers to a processin which more than one centrifugation step is used during separation ofthe polymer (e.g., PHA) from the biomass (see additional discussionbelow). For example, the residual biomass formed in the process in FIG.1 can be treated and ultimately centrifuged, thereby creating atwo-stage process (see, for example, FIG. 2 and discussion below).

In some embodiments, the process results in a relatively high yield ofthe PHA. For example, in some embodiments a ratio of the dry weight ofextracted PHA to the dry weight of the PHA initially contained in thebiomass is at least about 0.9 (e.g., at least about 0.95, at least about0.97, at least about 0.98). In certain embodiments, a relatively highyield of PHA can be achieved without using a multi-stage process (e.g.,with a one-stage process).

In certain embodiments, the process can be performed with relativelylarge amount of the solvent being transferred to the PHA phase. Forexample, in some embodiments a ratio of the volume of solvent recoveredin the PHA phase to the volume of solvent contacted with the biomass isat least about 0.8 (e.g., 0.85, at least about 0.9, at least about 0.95,at least about 0.98, at least about 0.99). In some embodiments, arelatively large amount of solvent can be transferred to the PHA phaseusing, for example, countercurrent conditions during separation of thepolymer (e.g., PHA) from the biomass.

In certain embodiments, the process can be performed with a relativelysmall amount of the solvent being transferred to the residual biomassphase. For example, in some embodiments a ratio of the volume of solventrecovered in the residual biomass phase to the volume of solventcontacted with the biomass is at most about 0.2 (e.g., at most about0.15, at most about 0.1, at most about 0.05, at most about 0.02, at mostabout 0.01). In some embodiments, a relatively small amount of thesolvent is transferred to the residual biomass phase using, for example,countercurrent conditions during separation of the polymer (e.g., PHA)from the biomass.

The slurry can be provided in any desired manner. Typically, the slurryis provided by forming a fermentation broth containing water and thebiomass, and removing a portion of the water from the fermentationbroth. The water can be removed, for example, by filtration (e.g.,microfiltration, membrane filtration) and/or by decanting and/or byusing centrifugal force. In certain embodiments, biomass impurities,such as cell wall and cell membrane impurities, can be removed duringthe process of providing the slurry. Such impurities can includeproteins, lipids (e.g., triglycerides, phospholipids, and lipoproteins)and lipopolysaccharides.

The PHA content of the biomass (e.g., PHA content of the dry biomass,inclusive of its polymer content, on a weight percent basis) can bevaried as desired. As an example, in embodiments in which the biomass isof microbial origin, the biomass can have a PHA content of at leastabout 50 weight percent (e.g., at least about 60 weight percent, atleast about 70 weight percent, at least about 80 weight percent). Asanother example, in embodiments in which the biomass is of plant origin,the biomass can have a PHA content of less than about 50 weight percent(e.g., less than about 40 weight percent, less than about 30 weightpercent, less than about 20 weight percent).

In some embodiments, the slurry has a solids content (e.g., dry biomass,inclusive of its PHA content, weight relative to total wet weight ofslurry) of from about 25 weight percent to about 40 weight percent(e.g., from about 25 weight percent to about 35 weight percent).

The biomass can be formed of one or more of a variety of entities. Suchentities include, for example, microbial strains for producing PHAs(e.g., Alcaligenes eutrophus (renamed as Ralstonia eutropha),Alcaligenes latus, Azotobacter, Aeromonas, Comamonas, Pseudomonads),genetically engineered organisms for producing PHAs (e.g., Pseudomonas,Ralstonia, Escherichia coli, Klebsiella), yeasts for producing PHAs, andplant systems for producing PHAs. Such entities are disclosed, forexample, in Lee, Biotechnology & Bioengineering 49:1-14 (1996); Braunegget al., (1998), J. Biotechnology 65: 127-161; Madison and Huisman, 1999;and Snell and Peoples 2002, Metabolic Engineering 4: 29-40, which arehereby incorporated by reference.

In embodiments in which the biomass contains microbial cells, the sizeof the microbial cells contained in the biomass can also be varied asdesired. In general, the microbial cells (e.g., bacterial cells) have atleast one dimension with a size of at least about 0.2 micron (e.g., atleast about 0.5 micron, at least about one micron, at least about twomicrons, at least about three microns, at least about four microns, atleast about five microns). In certain embodiments, using relativelylarge microbial cells (e.g., relatively large bacterial cells) in thebiomass can be advantageous because it can facilitate the separation ofthe biomass to form the biomass slurry.

In general, a PHA is formed by polymerization (e.g., enzymaticpolymerization) of one or more monomer units. Examples of such monomerunits include, for example, 3-hydroxybutyrate, 3-hydroxypropionate,3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate,3-hydroxyoctanoate, 3-hydroxynonaoate, 3-hydroxydecanoate,3-hydroxydodecanoate, 3-hydroxydodecenoate, 3-hydroxytetradecanoate,3-hydroxyhexadecanoate, 3-hydroxyoctadecanoate, 4-hydroxybutyrate,4-hydroxyvalerate, 5-hydroxyvalerate, and 6-hydroxyhexanoate.

In some embodiments, the PHA has at least one monomer unit with thechemical formula —OCR₁R₂(CR₃R₄)_(n)CO—. n is zero or an integer (e.g.,one, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13,14, 15, etc.). Each of R₁, R₂, R₃ and R₄ is a hydrogen atom, a saturatedhydrocarbon radical, an unsaturated hydrocarbon radical, a substitutedradical (e.g., a substituted hydrocarbon radical) or an unsubstitutedradical (e.g., an unsubstituted hydrocarbon radical). Examples ofsubstituted radicals include halo-substituted radicals (e.g., halosubstituted hydrocarbon radicals), hydroxy-substituted radicals (e.g.,hydroxy-substituted hydrocarbon radicals), halogen radicals,nitrogen-substituted radicals (e.g., nitrogen-substituted hydrocarbonradicals) and oxygen-substituted radicals (e.g., oxygen-substitutedhydrocarbon radicals). Substituted radicals include, for example,substituted, saturated hydrocarbon radicals and substituted, unsaturatedhydrocarbon radicals. R₁ is the same as or different from each of R₂, R₃and R₄. R₂ is the same as or different from each of R₁, R₃ and R₄. R₃ isthe same as or different from each of R₂, R₁ and R₄, and R₄ is the sameas or different from each of R₂, R₃ and R_(1.)

In some embodiments, the PHA is a copolymer that contains two or moredifferent monomer units. Examples of such copolymers includepoly-3-hydroxybutyrate-co-3-hydroxypropionate,poly-3-hydroxybutyrate-co-3-hydroxyvalerate,poly-3-hydroxybutyrate-co-3-hydroxyhexanoate,poly-3-hydroxybutyrate-co-4-hydroxybutyrate,poly-3-hydroxybutyrate-co-4-hydroxyvalerate,poly-3-hydroxybutyrate-co-6-hydroxyhexanoate, poly3-hydroxybutyrate-co-3-hydroxyheptanoate,poly-3-hydroxybutyrate-co-3-hydroxyoctanoate,poly-3-hydroxybutyrate-co-3-hydroxydecanoate,poly-3-hydroxybutyrate-co-3-hydroxydodecanotate,poly-3-hydroxybutyrate-co-3-hydroxyoctanoate-co-3-hydroxydecanoate,poly-3-hydroxydecanoate-co-3-hydroxyoctanoate, andpoly-3-hydroxybutyrate-co-3-hydroxyoctadecanoate.

In certain embodiments, the PHA is a homopolymer. Examples of suchhomopolymers include poly-4-hydroxybutyrate, poly-3-hydroxypropionate,poly-3-hydroxybutyrate, poly-3-hydroxyhexanoate,poly-3-hydroxyheptanoate, poly-3-hydroxyoctanoate,poly-3-hydroxydecanoate and poly-3-hydroxydodecanoate.

The PHA can have a polystyrene equivalent weight average molecularweight of at least about 500 (e.g., at least about 10,000, at leastabout 50,000) and/or less than about 2,000,000 (e.g., less than about1,000,000, less than about 800,000).

In general, the amount of solvent system added to the slurry can bevaried as desired. In certain embodiments, an amount of solvent systemis added to the slurry so that, after centrifugation, the PHA phase hasa PHA solids content of less than about 10 weight percent (e.g., lessthan about eight weight percent, less than about six weight percent,less than about five weight percent, less than about four weightpercent, less than about three weight percent).

The solvent system includes one or more solvents for the PHA, and canoptionally include one or more precipitants for the PHA. Without wishingto be bound by theory, it is believed that including a precipitant forthe PHA in the solvent system can reduce the viscosity of the solutioncontaining the polymer and the solvent system and/or enhance theselectivity of the process in extracting the desired PHA.

In general, a solvent for a given polymer is capable of dissolving thepolymer to form a substantially uniform solution at the molecular orionic size level. In general, a precipitant for a given polymer iscapable of inducing the precipitation of the polymer and/or weakeningthe solvent power of a solvent for the polymer.

The choice of solvent(s) and/or precipitant(s) generally depends on thegiven PHA to be purified. Without wishing to be bound by theory, it isbelieved that an appropriate solvent for a given polymer can be selectedby substantially matching appropriate salvation parameters (e.g.,dispersive forces, hydrogen bonding forces and/or polarity) of the givenpolymer and solvent. Such solvation parameters are disclosed, forexample, in Hansen, Solubility Parameters—A User's Handbook, CRC Press,N.Y., N.Y. (2000).

In certain embodiments in which the PHA is a poly-3-hydroxybutyratecopolymer (e.g., poly-3-hydroxybutyrate-co-3-hydroxypropionate,poly-3-hydroxybutyrate-co-3-hydroxyvalerate,poly-3-hydroxybutyrate-co-3-hydroxyhexanoate and/orpoly-3-hydroxybutyrate-co-4-hydroxybutyrate,poly-3-hydroxybutyrate-co-3-hydroxyoctanoate-co-3-hydroxydecanote-co-3-hydroxydodecanote),where the majority of the monomer units are 3-hydroxybutyrate (e.g., atleast about 50% of the monomer units are 3-hydroxybutyrate, at leastabout 60% of the monomer units are 3-hydroxybutyrate), the solvent(s)may be selected from ketones, esters and/or alcohols with at least fourcarbon atoms, and the precipitant(s) may be selected from alkanes,methanol and ethanol.

In some embodiments in which the PHA is poly-3-hydroxyoctanoate, thesolvent(s) may be selected from ketones, esters, alcohols with at leastfour carbon atoms or alkanes (e.g., hexane).

In general, the ketones can be cyclic or acyclic, straight-chained orbranched, and/or substituted or unsubstituted. Examples of acyclicketones and cyclic ketones include methyl isobutyl ketone (“MIBK”),3-methyl-2-pentanone (butyl methyl ketone), 4-methyl-2-pentanone (methylisobutyl ketone), 3-methyl-2-butanone (methyl isopropyl ketone),2-pentanone (methyl n-propyl ketone), diisobutyl ketone, 2-hexanone(methyl n-butyl ketone), 3-pentanone (diethyl ketone),2-methyl-3-heptanone (butyl isopropyl ketone), 3-heptanone (ethyln-butyl ketone), 2-octanone (methyl n-hexyl ketone),5-methyl-3-heptanone (ethyl amyl ketone), 5-methyl-2-hexanone (methyliso-amyl ketone), heptanone (pentyl methyl ketone), cyclo-pentanone,cyclo-hexanone.

In general, the esters can be cyclic or acyclic, straight-chained orbranched, and/or substituted or unsubstituted. Examples of acyclicesters and cyclic esters include ethyl acetate, propyl acetate, butylacetate, amyl acetate, butyl iso-butyrate, methyl n-butyrate, butylpropionate, butyl butyrate, methyl valerate, ethyl valerate, methylcaproate, ethyl butyrate, ethyl acetate, gamma-butyrolactone,gamma-valerolactone.

In general, the alcohols having at least four carbon atoms can be cyclicor acyclic, straight-chained or branched, and/or substituted orunsubstituted. Examples of such cyclic alcohols and acyclic alcoholsinclude methyl-1-butanol, ethyl-1-butanol, 3-methyl-1-butanol (amylalcohol), 2-methyl-1-pentanol, 2-methyl-2-butanol (amyl alcohol),3-methyl-2-pentanol (methyl iso-butyl carbinol), methyl-2-pentanol,4-methyl-2-pentanol, butyl alcohol, pentyl alcohol, hexyl alcohol,heptyl alcohol, cyclo-hexanol, methyl-cyclo-hexanol and fusel oil (amixture of higher alcohols, which is often a by-product of alcoholdistillation, and typically is predominantly amyl alcohol (methylbutanol)).

In general, the alkanes can be cyclic or acyclic, straight-chained orbranched, and/or substituted or unsubstituted. In some embodiments, thealkanes include straight-chain alkanes and have five or more carbonatoms (e.g., heptane, hexane, octane, nonane, dodecane). In certainembodiments the alkanes include isoalkanes (e.g. methyl heptane, methyloctane, dimethyl heptane). In certain embodiments, Soltrol® 100 (amixture of C9-C11 isoalkanes, commercially available from ChevronPhillips Chemical Company located in Houston, Tex.) can be used.

Generally, the amount of solvent present in the solvent system can bevaried as desired. In certain embodiments, the solvent system has atleast about five parts (e.g., at least about 10 parts, at least about 15parts) solvent per part PHA and/or less than about 50 parts (e.g., lessthan about 30 parts, less than about 25 parts) solvent per part PHA.

In some embodiments, a solvent for the PHA is non-halogenated. Using anon-halogenated solvent can be advantageous because this can reduce thenegative environmental impact of the solvent, reduce the health risksassociated with using the solvent, and/or reduce the costs associatedwith storing, handling and/or disposing the solvent.

In certain embodiments, a solvent for the PHA can have a relatively lowdensity. For example, a solvent for the PHA can have a density of lessthan about 0.95 kilograms per liter (e.g., less than about 0.9 kilogramsper liter, less than about 0.8 kilograms per liter, less than about 0.7kilograms per liter) at 20° C. Without wishing to be bound by theory, itis believed that using a relatively low density solvent can enhance thequality of the separation of the PHA phase from the residual biomassphase.

In some embodiments, a solvent for the PHA has a relatively lowsolubility in water. For example, a solvent for the PHA can have asolubility in water of less than about one percent (e.g., less thanabout 0.5 percent, less than about 0.2 percent) at 20° C. A solvent witha relatively low solubility in water can be desirable because such asolvent is less likely to intermix with water. This can enhance the easeof providing two separate phases during the process, thereby reducingthe cost and/or complexity of the process.

In certain embodiments, a solvent for the PHA is substantiallynon-hydrolyzable. For example, the solvent can be at most ashydrolyzable as ethyl acetate. Using a substantially non-hydrolyzablesolvent can reduce the likelihood of undesirable side product formation(e.g., chemically reactive species, such as organic acids). This canreduce the amount and/or rate of, for example, corrosion of portions(e.g., plumbing) of the system in which the PHA extraction is performed.

In some embodiments, a solvent for the PHA is relatively easily strippedfrom water. For example, the solvent can have a logK value relative towater at 100° C. of at least about 1.5 (e.g., at least about 1.8, atleast about two, at least about 2.2) as determined according to Hwang etal., Ind. Eng. Chem. Res., Vol. 31, No. 7, pp. 1753-1767 (1992), whichis hereby incorporated by reference. Using a solvent that is readilystripped from water can be desirable because such a solvent can be morereadily recovered and recycled relative to other solvents that are notas readily stripped from water.

In certain embodiments, a solvent for the PHA has a boiling pointgreater than 100° C.

In certain embodiments, an appropriate solvent is non-halogenated, hasrelatively low (e.g., less than ethyl acetate) water solubility, andrelatively low reactivity from the perspective of hydrolysis and/or fromthe perspective of reactivity towards the polymer.

In some embodiments, the solubility of the PHA in the precipitant isless than about 0.2 percent (e.g., less than about 0.1 percent) of thePHA at 20° C.

In certain embodiments, a relatively small volume of precipitant isadded to the PHA phase relative to the volume of solvent system added tothe slurry. For example, the ratio of the volume of precipitant added tothe PHA phase to the volume of solvent system added to the slurry isless than about 0.2 (e.g., less than about 0.1, less than about 0.07,less than about 0.05).

In embodiments in which the solvent system contains one or more solventsfor PHA and one or more precipitants for PHA, the solvent(s) and theprecipitant(s) can have a relative volatility of at least about two(e.g., at least about three, at least about four) at the equimolarbubble point of the solvent(s) and the precipitant(s) at atmosphericpressure.

In some embodiments in which the solvent system contains one or moresolvents for the PHA and one or more precipitants for the PHA, thesolvent(s) and the precipitant(s) do not form an azeotrope. Usingsolvent(s) and precipitant(s) that do not form an azeotrope can bedesirable because it can be easier to separate and recover the solventand precipitant for re-use relative to a solvent and precipitant thatform an azeotrope.

In certain embodiments in which the solvent system contains a solventfor the PHA and a precipitant for the PHA, the solution formed of thePHA and the solvent system contains less than about 25 volume percent(e.g., less than about 20 volume percent, less than about 15 volumepercent, less than about 10 volume percent) of the precipitant.

In general, the mixture containing the solvent system and the slurry isheated to enhance the interaction of the solvent system with the PHA,thereby allowing the PHA to be removed from the biomass.

In general, the temperature of the solvent system and slurry mixtureduring agitation can be varied as desired. In some embodiments, thetemperature is less than about 160° C. (e.g., less than about 125° C.,less than about 95° C., less than about 65° C.) and/or at least about20° C. In certain embodiments, the temperature is from ambienttemperature to about 95° C. (e.g., from about 40° C. to about 80° C.,from about 60° C. to about 70° C.). In certain embodiments the pressurecan be regulated to greater than atmospheric pressure to facilitateextraction at elevated temperature (e.g. greater than 1 atmosphere, upto 20 atmosphere).

Generally, the shear force used when agitating the solvent system andslurry mixture can be varied as desired. In certain embodiments, thesolvent system and slurry mixture is agitated by stirring so that thedissolution time is reduced. In some embodiments, to assist dissolution,a high shear impeller and agitator (e.g. flat blade impeller such as the6 bladed Rushton turbine) can be used at tip speeds of, for example,about five meters per second or more (e.g., to about 10 meters persecond). In certain embodiments a high speed disperser having a lowprofile blade can be used at tip speeds of, for examples, about 10 meterper second or more (e.g. about 15 meter per second or more, about 20meter per second to about 25 meter per second), Typically, the highspeed dispersers have a blade with a low profile bladed or saw toothedge to generate high shear at enhanced tip speeds. In certainembodiments, a rotor/stator system is used that generates relativelyhigh shear (e.g., at tip speeds up to about 50 meters per second) in thegap between a high speed rotor that spins within a slotted stator. Ingeneral the geometry of the rotor and stator can be varied to suitparticular applications and many designs are commercially available.

In general, the solvent system and slurry mixture is agitated until acentrifuged sample of the mixture has a PHA phase with a desired PHAsolids content. In some embodiments, the solvent system and slurrymixture is agitated for less than about three hours (e.g., less thanabout two hours) and/or at least about one minute (e.g., at least about10 minutes, at least about 30 minutes).

In certain embodiments, the PHA phase contains less than about 0.5weight percent (e.g., less than about 0.25 weight percent, less thanabout 0.1 weight percent) biomass relative to the amount of dissolvedPHA in the PHA phase.

In some embodiments, the biomass phase contains less than about 25weight percent (e.g., less than about 20 weight percent, less than about15 weight percent) of the solvent that was initially present in thesolvent system and or at least about one weight percent (e.g., at leastabout five weight percent, at least about 10 weight percent) of thesolvent that was initially present in the solvent system.

In some embodiments, the PHA phase has a relatively low viscosity. Forexample, this phase can have a viscosity of less than about 100centipoise (e.g., less than about 75 centipoise, less than about 50centipoise, less than about 40 centipoise, less than about 30centipoise). Without wishing to be bound by theory, it is believed thatpreparing the PHA phase such that it has a relatively low viscosity canresult in a relatively good separation of the PHA phase from theresidual biomass phase. In particular, it is believed that the rate ofseparation of the phases during centrifugation is inversely proportionalto the viscosity of the PHA phase so that, for a given centrifugationtime, decreasing the viscosity of the PHA phase results in an improvedseparation of the phases relative to certain systems in which the PHAphase has a higher viscosity.

In certain embodiments, the PHA phase has a relatively high polymerconcentration. For example, the PHA phase can have a polymerconcentration of at least about two percent (e.g., at least about 2.5percent, at least about three percent, at least about 3.5 percent, atleast about four percent, at least about 4.5 percent, at least aboutfive percent).

Various types of devices can be used that exploit centrifugal force. Asan example, in some embodiments centrifugation is performed using a discstack (e.g., a model SC-6, available from Westfalia Separator US, Inc.,located in Northvale, N.J.). In certain embodiments centrifugation isperformed using a decanter (e.g., a model CA-220, available fromWestfalia Separator US, Inc., located in Northvale, N.J.). In someembodiments, a hydroclone can be used.

In certain embodiments a countercurrent centrifugal contacter (e.g., aPodbielniak centrifugal contacter, a Luwesta centrifugal contacter,Taylor-Couette centrifugal contacter) can be used. In general, acountercurrent centrifugal contacter is used by having two (or possiblymore) fluid streams contact each other. One stream (the solvent stream)begins as a fluid stream that is relatively rich in solvent. Anotherstream (the biomass stream) begins as a fluid stream that is relativelyrich in PHA. The two streams contact each other under countercurrentconditions such that a portion of the solvent stream that is richest insolvent contacts a portion of the biomass stream that is poorest in PHA(to enhance, e.g., optimize, the recovery of PHA from the biomassstream), and/or such that a portion of the biomass stream that isrichest in PHA contacts a portion of the solvent stream that is mostladen with PHA (to enhance, e.g., optimize, the concentration of PHA inthe solvent stream). In certain embodiments, this is achieved by flowingthe solvent stream reverse to the biomass stream (reverse flowconditions). Countercurrent centrifugal contacters are available from,for example, B&P Process Equipment (Saginaw, Mich.) and Quadronics.Examples of commercially available countercurrent centrifugal contactersinclude the Podbielniak A-1 countercurrent centrifugal contacter (B&PProcess Equipment) and the Podbielniak B-10 countercurrent centrifugalcontacter (B&P Process Equipment).

In general, the conditions (e.g., force, time) used for centrifugationcan be varied as desired.

In some embodiments in which a disc stack is used, centrifugation can beperformed using at least about 5,000 RCF (Relative Centrifugal Force)(e.g., at least about 6,000 RCF, at least about 7,000 RCF, at leastabout 8,000 RCF) and/or less than about 15,000 RCF (e.g., less thanabout 12,000 RCF, less than about 10,000 RCF). In certain embodiments inwhich a decanter is used, centrifugation can be performed using at leastabout 1,000 RCF (e.g., at least about 1,500 RCF, at least about 2,000RCF, at least about 2,500 RCF) and/or less than about 5,000 RCF (e.g.,less than about 4,000 RCF, less than about 3,500 RCF). In certainembodiments in which a countercurrent centrifugal contacter is used,centrifugation can be performed using at least about 1,000 RCF (e.g., atleast about 1,500 RCF, at least about 2,000 RCF, at least about 2,500RCF) and/or less than about 5,000 RCF (e.g., less than about 4,000 RCF,less than about 3,500 RCF).

In some embodiments in which a disc stack is used, centrifugation can beperformed for less than about one hour (e.g., less than about 30minutes, less than about 10 minutes, less than about five minutes, lessthan about one minute) and/or at least about 10 seconds (e.g., at leastabout 20 seconds, at least about 30 seconds). In certain embodiments inwhich a decanter is used, centrifugation can be performed for less thanabout one hour (e.g., less than about 30 minutes, less than about 10minutes, less than about five minutes, less than about one minute)and/or at least about 10 seconds (e.g., at least about 20 seconds, atleast about 30 seconds). In certain embodiments in which acountercurrent centrifugal contacter is used, centrifugation can beperformed for less than about one hour (e.g., less than about 30minutes, less than about 10 minutes, less than about five minutes, lessthan about one minute) and/or at least about 10 seconds (e.g., at leastabout 20 seconds, at least about 30 seconds).

After centrifugation, a precipitant for the PHA is added to theseparated PHA phase to form a mixture. In embodiments in which thesolvent system contains one or more precipitants for the PHA, theprecipitant added to the separated PHA phase may be the same as ordifferent from the precipitant(s) contained in the solvent system.

In general, the amount of the precipitant added to the separated PHAphase can be varied as desired. In some embodiments, the amount ofprecipitant added to the separated PHA phase is at least about 0.1 part(e.g., at least about 0.25 part, at least about 0.5 part) precipitant byvolume relevant to the volume of solvent in the PHA phase and/or lessthan about two parts (e.g., less than about 1.5 parts, less than aboutone part, less than about 0.75 part) precipitant by volume relevant tothe volume of solvent in the PHA phase.

The PHA phase/precipitant mixture is agitated to enhance the interactionof the PHA with the precipitant for the PHA. This allows the PHA toprecipitate from the mixture, resulting in a combination formed ofprecipitated PHA and a mixture containing the solvent system and theadded precipitant for the PHA. In general, agitation of the PHAphase/precipitant mixture is performed at room temperature, but othertemperatures can be used if desired. In some embodiments, the PHAphase/precipitant mixture is mixed using high shear devices such as highshear impellers (e.g.; a six-bladed Rushton turbine), high speeddispersers and rotor/stator high shear in-line or in-tank mixers. Theshear rates are determined by the tip speeds of the various devices andcan be varied between, for example, from about five meters per second toabout 50 meters per second (e.g., from about 10 meters per second toabout 25 meters per second). Without wishing to be bound by theory, itis believed that the high shear mixing can, under certain conditions,improve the quality of the precipitated polymer.

The precipitated PHA is then separated from the remaining liquid (e.g.,solvent system and precipitant). This separation can be performed by,for example, filtration or centrifugation (e.g., using a basketcentrifuge, using a vacuum belt filter).

Typically, the precipitated PHA is then washed to assist removingundesired impurities, such as remaining solvent and/or precipitant. Insome embodiments, the polymer can be washed with solvent (e.g.,relatively freshly prepared solvent), such as, for example, a mixture ofthe PHA solvent and the PHA precipitant (e.g., with any ratio between0-100%). Usually, the composition for washing is selected to reduce(e.g., minimize) the re-dissolution of the polymer and/or to enhance(e.g., maximize) removal of impurities. In certain embodiments, theappropriate ratio can be dependent on the particular polymer compositionand/or can be determined by standard experimentation (washingefficiency). In some embodiments this washing step can be conducted atelevated temperature and appropriate residence time to furtherfacilitate the washing and removal of impurities.

Typically, the washed, precipitated PHA is dried (e.g., at a temperatureof from about 40° C. to about 100° C.). Drying can be performed undervacuum (e.g., to assist in facilitating recovery of the residualsolvent). In certain embodiments it may be desirable to directly extrudethe precipitated polymer still containing solvent in, for example, adevolatilizing extruder. Such extrusion can be performed, for example,at a temperature close to the polymer melting point, and the solvent canbe recovered directly from the extruder. Water can optionally beinjected under pressure into the devolatilizing extruder (e.g., togenerate steam in-situ to facilitate efficient stripping and removal oftraces of residual solvent). A gas stream (e.g. air, CO₂ or steam) canoptionally be injected into the extruder (e.g., to facilitate solventremoval). Extrusion can consolidate drying and product formation (e.g.pelletizing) operations into a single unit with, for example, capitaland process operating cost savings.

The remaining liquid (solvent system and precipitant) can be furtherprocessed so that the components of the liquid (solvent(s) and/orprecipitant(s)) can be re-used. For example, the liquid can be distilledto separate solvent from precipitant. In some embodiments, the separatedsolvent and/or precipitant can be re-used in the process described above(e.g., as a solvent in the solvent system, as a precipitant in thesolvent system, as a precipitant added to the PHA phase). In certainembodiments, the separated solvent and/or precipitant can be re-used inthe process described in FIG. 2 (see discussion below) (e.g., as asolvent in the solvent system, as a precipitant in the solvent system,as a precipitant added to the PHA phase).

In certain embodiments, the process (or portions of the process) can beperformed in a continuous and/or an in-line manner. As an example, theprocess can involve an in-line rotor/stator process for dissolution,and/or an in-line rotor/stator process for precipitation of the PHAand/or an in-line devolatilizing extruder (e.g. a Werner and PfleidererZSK extruder supplied by Coperion Corporation of Ramsey, N.J.) forremoving the solvent and forming PHA solids (e.g. pellets).

In some embodiments, the process uses the solvent in a relativelyefficient manner. For example, at least about 90 volume percent (e.g.,at least about 95 volume percent, at least about 97 volume percent, atleast about 98 volume percent) of the solvent initially used in thesolvent is recovered for re-use.

In certain embodiments, the process uses the precipitant in a relativelyefficient manner. For example, at least about 90 volume percent (e.g.,at least about 95 volume percent, at least about 97 volume percent, atleast about 98 volume percent) of the combined amount of precipitantinitially used in the solvent and added to the PHA phase is recoveredfor re-use.

FIG. 2 is a flow diagram showing an embodiment of a second stage of atwo-stage process that can be used to enhance the efficiency of PHAextraction by extracting at least a portion of the PHA present in theresidual biomass phase (FIG. 1). As shown in FIG. 2, a solvent system isadded to the biomass phase to provide a mixture containing the biomassphase and the solvent system. The mixture is agitated (e.g., using theconditions described above with respect to agitation of the slurry andsolvent system mixture) to provide a combination including a PHA phase(containing predominantly solvent system and PHA) and a biomass phase(containing predominantly biomass, water and carry-over solvent system).The PHA phase and biomass phase are separated using centrifugation(e.g., using the conditions described above with respect to centrifugingthe PHA phase and biomass phase). The PHA phase can be treated asdescribed above (e.g., by adding a precipitant for the PHA, agitating,separating, washing, drying), or the PHA phase can be added to theslurry and solvent mixture described above. The components of thesolvent system (e.g., solvent(s) and/or precipitant(s)) can be strippedfrom the remaining biomass phase using standard techniques. The residualsolvent contained in the biomass can be recovered through a variety ofmeans such as steam stripping in a suitable column, a desolventizingdrier (e.g. desolvantizer toaster used commonly in recovering residualsolvent from soybean meal after oil extraction) or direct drying withsolvent recovery (e.g. vacuum drier, fluid bed drier with inert gascirculation and solvent condensation). In some embodiments, the biomasscontaining the solvent can be co-dried with a compatible animal feedmaterial (e.g., gluten feed, distiller dry grain, oil seed meal) in adrier that is suitably rated to handle and recover and/or safelyeliminate (e.g. adsorption or incineration) the residual solvent. In theoverall process in FIG. 2, the first stage is shown in FIG. 1, and thesecond stage is shown in FIG. 2. In certain embodiments, the residualbiomass can be used as a nutrient for fermentation (e.g. ethanolfermentation using Saccharomyces), optionally after removing theresidual solvent as described above. In some embodiments, the biomasscan be hydrolyzed (e.g. by exposure to acidic conditions at elevatedtemperature, treatment with protease enzymes, lytic enzymes) to improveits nutrient profile for fermentation.

While certain methods for extracting a PHA from biomass have beendescribed, other embodiments are also possible.

As an example, dry biomass can be used. In some embodiments, the drybiomass can be combined with water to provide a slurry.

As another example, a precipitant for the PHA can be added to the slurrybefore adding the solvent system. In some embodiments, the amount ofprecipitant added is at least about 0.5 volumes (e.g., from about 0.5volumes to about two volumes) relative to the slurry.

Adding precipitant before adding the solvent system can resuit in theformation of a relatively pure isolated, extracted PHA (e.g., a purityof at least about 99%, a purity of at least about 99.5%, at purity of atleast about 99.9%). The polymer purity can be determined by gaschromatography (GC) analysis (e.g., with a Hewlett Packard 5890 SeriesII GC equipped with Supelco 24044 SBP™-1 column of 30 m×0.32 mm ID with0.25 μm film) following butanolysis of the polymer sample under acidicconditions to form butyl esters of the PHA monomeric units as well asthe butyl esters of the lipids and phospholipids fatty acid residues.Suitable standards of the fatty acids and hydroxy acids (e.g. palmiticacid, stearic acid, oleic acid, linoleic acid and 3-hydroxy butyricacid) are used to calibrate and standardize and quantify thechromatographic response. This can be used to quantify both the polymercontent as well as the impurity content. Inorganic impurities can bequantified by ashing.

Without wishing to be bound by theory, it is believed that adding aprecipitant for the PHA to the slurry prior to adding the solvent systemcan assist in removing biomass impurities present in the biomass (e.g.,phospholipids, neutral lipids, lipoproteins). This can be particularlyadvantageous if the PHA solids content in the biomass is relatively high(e.g., a PHA solids content of at least about 65%, at least about 75%).

As a further example, the biomass and/or the slurry can be chemicallypre-treated for example with relatively mild caustic conditions (e.g., apH of from about 8.5 to 10, from about 8.5 to about 9, from about 9 toabout 9.5, from about 9.5 to about 10) followed by neutralization beforeadding the solvent system. This can result in the formation of arelatively pure isolated, extracted PHA (e.g., a purity of at leastabout 99%, at least about 99.5%). The caustic conditions can be preparedusing one or more relatively basic materials, such as, for example,potassium hydroxide, sodium hydroxide and/or ammonium hydroxide.

As another example, the temperature can be elevated (e.g. anytemperature between room temperature and about 95° C.) and otherchemicals such as surfactants, detergents and/or enzymes added duringthe chemical pre-treatment step to further facilitate the formation of arelatively pure isolated, extracted PHA (e.g., a purity of at leastabout 99%, at least about 99.5%).

Without wishing to be bound by theory, it is believed that a chemicaltreatment (e.g., a relatively mild caustic treatment) of the slurryprior to adding the solvent system can assist in removing biomassimpurities present in the biomass (e.g., lipids, phospholipids,lipoproteins). This can be particularly advantageous if the PHA solidscontent in the biomass is relatively high (e.g., a PHA solids content ofat least about 65%, at least about 75%).

As another example, the methods can include concentration (e.g.,evaporation) of the PHA phase after separation of this phase from theresidual biomass phase but before addition of the precipitant for thePHA to the PHA phase. This can reduce the volume of solution, therebyreducing precipitant.

As a further example, in some embodiments the processes can be performedwithout adding a precipitant for the PHA to the PHA phase.

Moreover, the solvent system can be formed and then contacted with thebiomass, or the biomass can be contacted with fewer than all thecomponents of the solvent system, followed by subsequent addition of theremaining portion of the solvent system (e.g., in series or all atonce). For example, in embodiments in which the solvent system includesa solvent for the PHA and a precipitant for the PHA, the slurry can becontacted with the solvent, followed by addition of the precipitant, orvice-versa. Alternatively, the solvent and precipitant can be combinedto form the solvent system, followed by contacting the biomass.

Furthermore, while the extraction of a single PHA from a biomass hasbeen described, the processes could be used to extract multiple PHAs(e.g., two, three, four, five, six) from a biomass. Such processes couldinvolve the use of multiple solvents, precipitants and/or solventsystems.

In addition, while solvent systems containing a single solvent for thePHA and optionally a single precipitant for the PHA have been described,multiple solvents for the PHA (e.g., two, three, four, five, six) and/ormultiple precipitants for the PHA (e.g., two, three, four, five, six)can be used.

As another example, in some embodiments the slurry/solvent systemmixture can be agitated without heating. Alternatively theslurry/solvent system mixture can be agitated under pressure withheating.

As a further example, the methods can include distilling the solventsystem/precipitant mixture formed (e.g., distilled) to separate thecomponents (e.g., solvent for the PHA, precipitant for the PHA) so thatone or more of the components can be re-used.

The following examples are illustrative and not intended to be limiting.In the examples, the chemicals were from Aldrich Chemical Co. Inc.(Milwaukee, Wis.), the overhead stirrer was an Ika®-werke Eurostar powercontrol-vise overhead stirrer (Ika Work Inc., Wilmington, N.C.), and thecentrifuge was a Sorvall RC 5B plus centrifuge.

EXAMPLE I

A batch of Escherichia coli biomass slurry containing 70% polymer on adry basis with a composition of polyhydroxybutyrate co 4-hydroxybutyratewith 25% 4-hydroxybutyrate was split three ways and treated as follows:

-   -   a. Spray dried and 30 g of dry biomass collected.    -   b. Spray dried, 30 g of biomass collected and re-wetted with        deionized (DI) water to 10 g.    -   c. 100 g of original slurry containing 30 g of dry biomass        without modification.

Each batch was extracted with 400 ml butyl acetate at room temperaturewith overhead stirring at 500 rpm for 2 hours. The resulting slurry wascentrifuged at 5000 g for 20 minutes and the PHA phase recovered. ThePHA content was determined by precipitation of the PHA from the PHAphase using hexane as precipitant followed by drying overnight undervacuum of one millimeter Hg and 40° C. The recovered polymer represented32% dissolution of the starting polymer (approach 1), 43% of thestarting polymer (approach 2), and greater than 97% dissolution of thestarting polymer (approach 3).

EXAMPLE II

In a side by side test broth from an Escherichia coli fermentationcontaining cells with one dimension exceeding 2 microns was compared toRalstonia eutropha containing cells with a maximum dimension of 0.5micron. The time to obtain a clear supernatant was determined at 12000rpm in an Eppendorf 5415C micro-centrifuge, using 1.5 mL centrifugetubes filled with 1 mL of broth. In the case of the E. coli broth clearsupernatant was obtained in less than 1 minute of centrifugation timewhile the Ralstonia eutropha required more than 5 minutes centrifugationfor similar clarity.

EXAMPLE III

A polymer solution containing 5% polymer by weight (expressed relativeto the total solution weight) was prepared by dissolving of Escherichiacoli biomass slurry containing 70% polymer on a dry basis with acomposition of polyhydroxybutyrate co 4-hydroxybutyrate with 25%4-hydroxybutyrate in butyl acetate (Aldrich Chemical Co. Inc.,Milwaukee, Wis.) using the procedure of Example Ic. The viscosity of theresulting solution was measured as 365 centiPoise (cP) using aBrookfield LVF Viscometer (Brookfield Engineering Laboratories Inc.,Stoughton, Mass.). For solutions with viscosity less than 100 cP, a No.1 spindle was used, and, for solutions with viscosity greater than 100cP, a No. 2 spindle was used. The solution was further diluted withadditional butyl acetate to 4% and 3% polymer by weight total solution.The resulting viscosities were found to be 150 cP and 40 cP,respectively.

Some of the 5% polymer solution in butyl acetate prepared above wassubsequently diluted using hexane (Aldrich Chemical Co. Inc., Milwaukee,Wis.) to prepare a 4.5%, 4.3%, 4.1% and 3.9% solution by weight. Theviscosities of these solutions were measured as described above anddetermined to be 215 cP, 37.5 cP, 5 cP and 27.5 cP, respectively.

The viscosities upon dilution of a 5% polymer solution in butyl acetatewith additional butyl acetate (PHA solvent) compared to dilution withhexane (PHA precipitant at room temperature) are depicted in FIG. 3.Dilution with the precipitant has a non-linear and desirable impact onreducing viscosity. The increased viscosity observed with hexanedilution to 3.9% by weight polymer in solution coincided with polymerprecipitation from solution at that level of hexane addition.

EXAMPLE IV

A recombinant E. coli was used to produce poly3-hydroxybutyrate-co-4-hydroxybutyrate (30% 4-hydroxybutyrate on a molarbasis) in a fed-batch fermentation, using glucose as the major carbonsource. At the completion of the fermentation the E. coli cells hadexpanded in size to greater than 2 microns in at least one dimension.The biomass accumulated 70% polymer on a dry weight basis. The biomasswas subsequently harvested using centrifugation to produce a wet biomasspellet, substantially free of dissolved impurities.

100 g of the wet biomass pellet (48% dry solids) containing 70% poly3-hydroxybutyrate co 4-hydroxybutyrate on a dry basis was charged with500 ml of ethyl acetate and agitated with a overhead stirrer at roomtemperature for 1 hour. The polymer composition was 30%4-hydroxybutyrate on a molar basis. The mixing time was terminated afterthe viscosity increased to the extent that further stirring was noteffective in mixing the material. A total of 350 ml of the slurry wascollected and centrifuged at 5000 g for a total of 20 minutes (SorvallRC 5B plus centrifuge, Kendro Laboratory Products, Newtown Conn.). Thetheoretical amount of ethyl acetate that should be recoverable from the350 mL of slurry was 300 mL according to mass balance calculations.

The PHA content of the PHA phase was about 5.3%. 220 milliliters of thePHA phase was recovered by decantation after centrifugation,constituting about 73% by volume of the total recoverable ethyl acetateof slurry prior to centrifugation.

EXAMPLE V

The preceding example was repeated, except butyl acetate (AldrichChemical Co. Inc., Milwaukee, Wis.) was used rather than ethyl acetate.The polymer in solution was about 4.3%. There was the appearance of anemulsified layer at the interface after centrifugation. 250 millilitersof the PHA phase was recovered by decantation after centrifugation,constituting about 83% of the total recoverable butyl acetate present inthe slurry before centrifugation.

EXAMPLE VI

The preceding example was repeated, except MIBK (Aldrich Chemical Co.Inc., Milwaukee, Wis.) was used rather than butyl acetate. The polymerin solution was about 4.2%. 290 milliliters of the PHA phase wasrecovered by decantation after centrifugation, constituting about 97% ofthe total recoverable MIBK present in the slurry before centrifugation.

EXAMPLE VII

100 g of wet E. coli biomass paste with 28% dry solids containing 75%Poly 3-hydroxybutyrate co 4-hydroxybutyrate with 35% 4-hydroxybutyrateon a dry solids basis was contacted with 200 g of hexane (AldrichChemical Co. Inc., Milwaukee, Wis.) and extracted for 2 hours withoverhead stirring (Ika®-werke Eurostar power control-visc overheadstirrer, Ika Work Inc., Wilmington, N.C.) at room temperature. Thehexane supernatant was separated by centrifugation at 3,500 g for 20minutes, and the solid pellet recovered after decanting the hexanesupernatant. The pellet was subsequently extracted using 425 g of MIBK(Aldrich Chemical Co. Inc., Milwaukee, Wis.) at room temperature withoverhead stirring (Ika®-werke Eurostar power control-visc overheadstirrer, Ika Work Inc., Wilmington, N.C.) for 3 hours. The supernatant(solution of polymer in MIBK) was separated by centrifugation at 3,500 gfor 20 minutes and the polymer precipitated by addition of 355 g ofhexane. The precipitated polymer was recovered by filtration using afunnel lined with fluted filter paper (VWR Scientific Products, WestChester, Pa.) and dried overnight at 45° C. under vacuum of 1 mm Hgunder vacuum in a Büchi rotavap to yield 13 gram of dried polymer. Thedried polymer was subjected to hot film pressing at 180° C. A suitableamount of PHA (typically 0.5 gram) is placed between two PET sheetsseparated by shims to form a film of 100 micron thickness. The filmassembly (i.e. two sheets, shims and PHA) was placed between the heated(180° C.) blocks of the press (Carver Hydraulic Press model #3912,Carver Inc., Wabash, Ind.) and a load of 10 tons was applied for 30seconds. The film was then cooled between aluminum blocks and theninspected for color and clarity. This yielded a substantially clear filmwith substantially no fuming or objectionable odors at the operatingtemperature of 180° C. during the press cycle.

EXAMPLE VIII

The preceding example was repeated, except that heptane (AldrichChemical Co. Inc., Milwaukee, Wis.) was used rather than hexane. Theprocessed yielded a substantially clear film with substantially nofuming or objectionable odors.

EXAMPLE IX

The preceding example was repeated, except that Soltrol® 100 (a mixtureof C₉-C₁₁ isoalkanes, commercially available from Chevron PhillipsChemical Company located in Houston, Tex.) was used instead of hexane.The process yielded a substantially clear film with substantially nofuming or objectionable odors.

EXAMPLE X

100 g of wet E. coli biomass paste with 28% dry solids containing 75%Poly 3-hydroxybutyrate co 4-hydroxybutyrate with 35% 4-hydroxybutyrateon a dry solids basis was treated with an effective 0.02 N of NaOH(Aldrich Chemical Co. Inc., Milwaukee, Wis.) at 65° C. for 20 minutesand thereafter rapidly cooled to room temperature over 5 minutes. Theresulting slurry was neutralized to pH of 7 using 85% phosphoric acid(Aldrich Chemical Co. Inc., Milwaukee, Wis.) and then centrifuged (3,500g) for 20 minutes, and washed with two volumes of DI water. Thesupernatant was discarded and the paste extracted using 425 g of MIBK atroom temperature with overhead stirring (Ika®-werke Eurostar powercontrol-visc overhead stirrer, Ika Work Inc., Wilmington, N.C.) forthree hours. The supernatant (solution of polymer in MIBK) was separatedby centrifugation at 3,500 g for 20 minutes and the polymer precipitatedby addition of 355 g of hexane. The precipitated polymer was recoveredby filtration and dried under vacuum in a Buchi B-171 rotavap (65° C.and 1 mm Hg vacuum for 8 hours) to yield 12 gram of dried polymer. Thedried polymer was subjected to hot film pressing at 180° C. This yieldeda film with only very slight discoloration/opaqueness.

EXAMPLE XI

The preceding example was repeated, but without the steps of treatingwith NaOH at 65° C. for 20 minutes and rapid cooling. The PHA thusrecovered yielded a film with strong yellow discoloration and opaquenessduring the hot film press. There was also evidence of thermaldegradation during the test as evidenced by fuming during the film testpressure cycle (180° C. and pressure of 10 tons of 30 seconds duration).

EXAMPLE XII

The following is an example of a one-stage process using acountercurrent centrifugal contacter.

11 kg of biomass paste containing 26% E. coli dry solids was contactedwith 38.6 kg methyl isobutyl ketone (4-methyl 2-pentanone or MIBK) forthree hours at 30° C. in a dissolution tank equipped with an agitatorwith marine impeller to maintain a homogeneous mixture. The biomasscontained 71% by weight ofpoly-3-hydroxybutyrate co 4-hydroxybutyrate(22% molar 4-hydroxybutyrate) on a dry basis. After three hours thesupernatant solution of MIBK and PHA obtained by centrifuging a samplefrom the dissolution tank contained 4.1% PHA by weight representing91.2% dissolution.

The mixture of cell paste and MIBK was fed to an A-1 pilot scalePodbielniak extractor (B&P Process Equipment, Saginaw, Mich.) as theheavy liquid in (HLI) at a rate of 635 ml/min. At the same time freshMIBK was fed as the light liquid in (LLI) to effect countercurrentwashing and extraction of the cell paste within the Podbielniakcontactor. The LLI was fed at a rate of 175 ml/min to maintain a feedratio of HLI:LLI of 3.6:1. A total of 49.6 kg of HLI and 12.8 kg of LLIwas fed over a 90 minute period. A total of 8.9 kg of residual cellpaste was collected as the heavy liquid out (HLO) and 53.6 kg of PHAsolution in MIBK was collected as the light liquid out (LLO) over thecourse of the 90 minute period. The LLO contained 3.75% by weight PHA insolution as determined by drying a sample of this material. A total of2.0 kg PHA was recovered in the LLO compared to the 2.04 kg PHAcontained in the HLI cell paste feed (98.4% overall recovery).

Mass balance measurements indicated that more than 98% of the total MIBKcontained in the combined HLI and LLI was recovered in the clarified PHAin MIBK solution (LLO). Laboratory centrifugation indicated that a veryclear interface was formed after 1 minute of centrifugation at 3000 g.The absence of any interfacial accumulation was also confirmed by theLLO remaining clear for the duration of the 90 minute trial.

The improved PHA recovery of the Podbielniak extractor (98.4%) comparedto that achieved with a single stage of dissolution (91.2%) confirms theefficacy of countercurrent contacting with fresh solvent to improve PHArecovery. The residual biomass paste viscosity is also reduceddramatically by countercurrent contacting as a result of the nearlycomplete removal of the PHA.

EXAMPLE XIII

The following is an example of PHA extraction using cyclo-hexanone.

90 g of wet E. coli biomass paste with 28% dry solids containing 80%poly 3-hydroxybutyrate co 4-hydroxybutyrate (PHA) with 12%4-hydroxybutyrate on a dry solids basis was added to 400 g ofcyclo-hexanone (Aldrich Chemical Co., Inc., Milwaukee, Wis.) at 90° C.The solution was homogenized for 5 minutes using a hand-held homogenizerequipped with a single slotted rotor stator combination at 30,000 rpm(Virtis, Gardiner, N.Y.) and then agitated for 30 minutes using anoverhead stirrer (Ika®-werke Eurostar power control-visc overheadstirrer, Ika Work Inc., Wilmington, N.C.). The temperature wascontrolled at 90±5° C. during the solvent contacting step. The biomasspaste/cyclo-hexanone mixture was then centrifuged at 3000 g for 5minutes to separate the supernatant (solution of polymer incyclo-hexanone) by decanting from the residual biomass paste pelletusing a Sorvall RC 5B plus centrifuge (Kendro Laboratory Products,Newtown, Conn.).

The supernatant was then re-heated in a beaker to 80±5° C. and an equalvolume of heptane (held at room temperature) was slowly added to thesolution over the course of 5 minutes while mixing vigorously with anoverhead stirrer (Ika®-werke Eurostar power control-visc overheadstirrer, Ika Work Inc., Wilmington, N.C.) to precipitate the polymerwhile maintaining the temperature between 70° C. and 80° C. Theprecipitated polymer was recovered by filtration using a funnel linedwith fluted filter paper (VWR Scientific Products, West Chester, Pa.)and air dried overnight in a chemical fume hood to yield 16 g of whitepolymer granules (80% overall recovery).

A film was prepared by placing approximately 0.5 g of polymer betweentwo PET sheets separated by shims to form a film of 100 micronthickness. The film assembly (i.e. two sheets, shims and PHA) was placedbetween the heated (180° C.) blocks of the press (Carver Hydraulic Pressmodel #3912, Carver Inc., Wabash, Ind.) and a load of 10 tons wasapplied for 30 seconds. The film was then cooled between aluminum blocksand inspected for color and clarity. This yielded a substantially clearfilm with substantially no fuming or objectionable odors at theoperating temperature of 180° C. during the press cycle.

EXAMPLE XIV

The following is an example of PHBH extraction.

Wet cell paste of Ralstonia eutropha (27% biomass solids on a weightbasis in water) containing approximately 65% poly 3-hydroxybutyrate co3-hydroxyhexanoate (PHBH) on a dry biomass basis with a composition of5-7% hydroxyhexanoate on a molar basis (Kichise et. al., (1999), Intl.J. Biol. Macromol. 25: 69-77) was prepared using a geneticallyengineered Ralstonia strain prepared as described in (Kichise et. al.,(1999), Intl. J. Biol. Macromol. 25: 69-77) and the fermentation processdescribed by Naylor in U.S. Pat. No. 5,871,980 using fructose and lauricacid as carbon sources. This biomass was added to a suitable quantity ofMIBK targeting a 5% solution (w/w) of PHBH in the solvent. The solutionwas homogenized for 5 minutes using a hand-held homogenizer equippedwith a single slotted rotor stator combination at 30,000 rpm (Virtis,Gardiner, N.Y.) and then agitated for 30 minutes using an overheadstirrer (Ika®-werke Eurostar power control-visc overhead stirrer, IkaWork Inc., Wilmington, N.C.). The temperature was controlled at 80±5° C.during the solvent contacting step. The resulting biomass/solventmixture was separated by centrifugation using a Sorvall RC 5B pluscentrifuge (Kendro Laboratory Products, Newtown, Conn.). The biomasspaste/cyclo-hexanone mixture was then centrifuged at 3000 g for 5minutes to separate the supernatant (solution of polymer incyclo-hexanone) by decanting from the residual biomass paste pellet.

The supernatant was added to a beaker and an equal volume of heptane wasslowly added to the solution over the course of 5 minutes while mixingvigorously with an overhead stirrer (Ika®-werke Eurostar powercontrol-visc overhead stirrer, Ika Work Inc., Wilmington, N.C.) toprecipitate the polymer. A white crystalline polymer powder wasrecovered after overnight drying in a chemical fume hood.

EXAMPLE XV

The following is an example of PHBX extraction.

Wet cell paste of genetically engineered Pseudomonas sp was prepared andgrown on glucose as described by Matsusakai et al., (1999,Biomacromolecules 1: 17-22) containing approximately 50% poly3-hydroxybutyrate co 3-hydroxyoctanoate co 3-hydroxydecanoateco3-hydroxydodecanoate co 3-hydroxydodecenoate (PHBX) on a dry biomassbasis with a composition of 92% 3-hydroxybutyrate, 1%3-hydroxyoctanoate, 3% 3-hydroxydecanoate, 3% 3-hydroxydodecanoate and1% 3-hydroxydodecenoate on a molar basis. This biomass was added to asuitable quantity of MIBK targeting a 5% solution (w/w) of PHBX in thesolvent. The solution was homogenized for 5 minutes using a hand-heldhomogenizer equipped with a single slotted rotor stator combination at30,000 rpm (Virtis, Gardiner, N.Y.) and then agitated for 30 minutesusing an overhead stirrer (Ika®-werke Eurostar power control-viscoverhead stirrer, Ika Work Inc., Wilmington, N.C.). The temperature wascontrolled at 80±5° C. during the solvent contacting step. The resultingbiomass/solvent mixture was separated by centrifugation using a SorvallRC 5B plus centrifuge (Kendro Laboratory Products, Newtown, Conn.). Thebiomass paste/cyclo-hexanone mixture was then centrifuged at 3000 g for5 minutes to separate the supernatant (solution of polymer incyclo-hexanone) by decanting from the residual biomass paste pellet.

The supernatant was added to a beaker and an equal volume of heptane wasslowly added to the solution over the course of 5 minutes while mixingvigorously with an overhead stirrer (Ika®-werke Eurostar powercontrol-visc overhead stirrer, Ika Work Inc., Wilmington, N.C.) toprecipitate the polymer. A white crystalline polymer powder wasrecovered after overnight drying in a chemical fume hood.

Other embodiments are in the claims.

1. A method of separating a polymer from a biomass containing thepolymer, the method comprising: contacting the biomass with a solventsystem, including a solvent for the polymer and a precipitant for thepolymer, to provide a residual biomass and a solution that includes thepolymer, the solvent for the polymer and the precipitant for thepolymer; and applying a centrifugal force to the solution and residualbiomass to separate at least some of the solution from the residualbiomass; wherein the polymer comprises a PHA and the method separatesthe polymer from the biomass.
 2. The method of claim 1, wherein thesolvent for the polymer has a density of less than about 0.95 kilogramsper liter.
 3. The method of claim 1, wherein the solvent for the polymeris non-halogenated.
 4. The method of chum 1, wherein the solvent for thepolymer has a solubility in water of than about one percent.
 5. Themethod of claim 1, wherein the solvent for the polymer is substantiallynon-hydrolyzable.
 6. The method of claim 1, wherein the solvent for thepolymer has a logK value relative to water at 100° C. of at least about1.5.
 7. The method of claim 1, wherein the solvent that has a boilingpoint greater than 100° C.
 8. The method of claim 1 wherein the solventfor the polymer is selected from the group consisting of ketones, estersand alcohols.
 9. The method of claim 1, wherein the solvent for thepolymer is selected from the group consisting of M1BK, butyl acetate,cyclo-hexanone and combinations thereof.
 10. The method of claim 1,wherein the precipitant for the polymer dissolves less than about 0.2%of the polymer at room temperature.
 11. The method of claim 1, whereinthe solvent for the polymer and the precipitant for the polymer have arelative volatility of at least about two at an equimolar bubble pointfor the solvent for the polymer and the precipitant for the polymer. 12.The method of claim 1, wherein the solvent for the polymer and theprecipitant for the polymer do not form an azeotrope.
 13. The method ofclaim 1, wherein the precipitant comprises at least one alkane.
 14. Themethod of claim 1, wherein the solution composes at most about 25% byvolume of the precipitant for the polymer.
 15. The method of claim 1,wherein the solution has a polymer concentration of at least about twopercent.
 16. The method of claim 1, wherein the solution has a viscosityor at most about 100 centipoise.
 17. The method of claim 1, wherein thebiomass containing the polymer is of microbial origin and has a polymercontent of at least about 50 weight percent.
 18. The method of claim 1,wherein the biomass containing the polymer is of plant origin and has apolymer content of less than about 50 weight percent.
 19. The method ofclaim 1, wherein the biomass containing the polymer comprises cells thatcontain the polymer.
 20. The method of claim 1, further comprisingremoving at least some of the polymer from the solution.
 21. The methodof claim 20, further comprising extruding the removed polymer to dry andpelletize the polymer.
 22. The method of claim 20, wherein removing thepolymer from the solution does not include exposing the solution to hotwater.
 23. The method of claim 20, wherein removing the polymer from thesolution includes adding a second precipitant for the polymer to thesolution.
 24. The method of claim 23, wherein the first and secondprecipitants for the polymer are the same.
 25. The method of claim 20,further comprising evaporating a portion of the solution before removingat least some of the polymer from the solution.
 26. The method of claim1, further comprising, after applying the centrifugal force to thesolution, adding a volume of a second precipitant for the polymer toremove at least some of the polymer from the solution, wherein thevolume of the second precipitant is less than about two parts relativeto the volume of the solvent system.
 27. The method of claim 1, whereinthe solvent system is contacted with the biomass under countercurrentflow conditions.
 28. The method of claim 27, wherein the method is aone-stage method.
 29. The method of claim 27, wherein the method is amulti-stage method.
 30. The method of claim 27, wherein thecountercurrent conditions include a pressure of at least about 65 psig.